1. Field of the Invention
The present invention relates to an apparatus for assembling a fuel assembly and more specifically to an apparatus for mechanically or automatically removing the keys after loading the fuel rods. The keys are inserted into support grids of a fuel assembly for deflecting the springs away from the dimples prior to loading the fuel rods into the supporting grids.
2. Background Technology
In general, pressurized light water nuclear reactors utilize a type of fuel assembly comprising: an upper nozzle and a lower nozzle; a plurality of supporting grids for supporting the fuel rods (shortened to grids henceforth) disposed between the nozzles with a certain spacing; instrumentation pipes and fuel rod guide pipes inserted into and attached to the grid cells of the grids; and a plurality of fuel rods inserted into and held elastically in the grid cells with the springs formed inside the grid cells.
When assembling such a fuel assembly, there is a danger of introducing scratches on the surface of the fuel rods if the rods are inserted into the grid cells with the springs and dimples as they are, because the springs and dimples are formed on the inside walls of the grid cells. To prevent damaging the surface of the fuel rods, there have been various methods suggested to deal with the prevention of surface damage problem.
For example, a method proposed in a U.S. Pat. No. 5,068,081 proposed the following fuel assembly. In this fuel assembly, key insertion opening are formed in the grids, and the spring deflection jigs are inserted into the grid cells to deflect the springs away from the dimples formed in each wall of the grid cell for elastically holding the fuel rod. The keys are inserted through the key openings to keep the springs in the deflected position, so as to allow the fuel rods to be inserted into the grid cells smoothly without the danger of causing surface damages.
However, such key insertion and removal operations are designed to be carried out manually, thus causing an operational problem because the tasks are cumbersome, the operations is lengthy and the efficiency is low. In particular, the workers involved in the key removal operation were required to work in the proximity of the fuel rods, and were particularly vulnerable to radiation exposure. From these viewpoints, there has been a need to automate the key removal operation.